We have lived in some moist environments and a favorite photo, while it otherwise looks good, has large parts of it that appear to have bonded to the glass of its frame. Presumably this is due to small amounts of condensation getting between the photo and the glass.
Does anyone know a trick I can use to help me separate them cleanly? The photo is about 16 years old.
Water does not harm photographic paper. After all, it is soaked in different waterbased chemicals during developing and washed in clean water in the end. So you'll be quite safe removing the glass along with the photo from the frame and sinking them in good clean lukewarm water with a couple of drops of liquid soap. Do not try to pry the photo off the glass by force. Gently rubbing the back of the photo should help water get in between the photo and glass. Expect result in a few minutes.
If the photo does not come free off the glass inside 20 minutes, it most likely is stuck forever. In that case take the photo with glass off the water, wipe all loose water away and take the suggested (in comments) photograph of the photo thru the glass now that you just washed the glass clean and the photo looks good while still wet.
Disclaimer. This is safe method for photos printed (developed) on normal photographic paper. If the photo in question is not of that material, soaking in water may in some cases do great harm and destroy the photo irreversably. You should take a photograph of the photo thru the glass before attempting any other operations. Advice on how to best do a photographic copy may be found elsewhere on this site.
Since I do photo restorations I frequently see the results of others efforts of trying to separate the photo from the glass.I personally do not try separating them. I do a high resolution flat bed scan through the glass and then rebuild the photo on my computer. This way my customer has both.
I agree with dpollitt, the parts of the photo stuck to the glass are most likely damaged beyond salvage. Although I've seen miracles come from someone who is well skilled in Photoshop!
That said, to separate the two from each other, I would first try using PEC-12 Photo Emulsion Cleaner.
You may also want to try and immersing the whole lot in a pan of distilled water. Using distilled water to prevent any damage from dissolved minerals. This may re-hydrate the stuck parts, and, as long as the print is not water soluble ink, just dry it quickly after and wipe it down with something like PEC-12.
If that doesn't work, as a last resort, I can only suggest using regular lighter fluid. I learned this trick from being a photo Grip for a catalog shop many years ago and would use lighter fluid to clean things like tape residue from all sorts of really expensive pieces of furniture and glass. I've also used it very successfully on other things like plastics and porcelain. All without any damage to anything.
If I had to guess, the slippery properties, and lighter fluid's ability to loosen things adhered to others come from it being petroleum based. But as mentioned, I would only do this as a last resort as I've never before applied it to a photograph.
I had the same issue with my son's photograph which was only in the frame for a year. Anyhow, soaking did nothing. Nor did heat from a hair dryer. I ended up losing parts of my picture to the glass which I then had to scrape off from the glass with a razor blade. Needless to say, I will be scanning in this school photograph prior to placing it in the frame.
I used a very sharp scraper blade. It got the picture off the glass with minimal damage. There was some, however. Maybe if I had soaked it AND used the scraper blade, it would have worked even better.
I got a strange idea not sure whether can work out for you. Besides the fluid, or water, or oil which you can used to soak the photo so that you can separate the picture from glass, trying to limit the damage to lowest level. You may try to user camera to take a photo before you do all those job. If the photo you take is good enough, you can wash out this new photo.
